The present invention relates generally to production apparatus used in the manufacture of color cathode ray picture tubes, and is particularly directed to improved means for automatically inserting a shadow mask into a face panel for engagement therewith.
With reference to FIG. 1, there is shown a mask assembly 10 oriented and aligned for insertion into a substantially rectangular face panel 12 including a rearwardly extending flange 13 with a plurality of inwardly extending studs 14, indicated as comprising three studs. Mask assembly 10 consists of a foraminated mask 15 which provides for color selection. The mask 15 is mounted on a rigid frame 16. A plurality of leaf-type suspension springs 18 equal in number to the studs 14 are spaced about the periphery of frame 16 for suspending mask 15 in precise adjacency to panel 12. Two of the springs are shown in this example as being located on opposing sides of the mask assembly 10, with the third spring located on an adjacent side. Four suspension springs 18 located on opposing sides of the frame may as well be used. One end of each of the springs 18 extends from the frame 16 in permanent attachment to the frame as by welding. The distal ends of the springs 16 have apertures 20 for detachably engaging associated ones of the studs 14. Face panel 12 has a phosphor-screen-bearing surface on the inner side thereof.
FIG. 2 shows the mask assembly 10 inserted into face panel 12 and detachably engaged thereto. The apertures 20 of the springs 18 are indicated as being engaged with associated studs 14. Engagement and disengagement of springs 18 with associated studs 14 is by movement of the distal ends of the springs 18 toward and away from the tube axis. When inserting and engaging the mask assemby 10 with the face panel 12, springs 18 must first be depressed toward frame 16. Each spring aperture 20 must be in alignment with the associated stud 14 before springs 18 can be released to provide engagement of the spring apertures 20 with the studs 14.
The perforations of shadow mask 15 may, in one common configuration, comprise a pattern of vertical perforations 28, shown schematically and greatly enlarged in FIG. 2, with a registered pattern of phosphor stripes 30, also shown greatly enlarged, deposited on inner surface 22 of face panel 12. The phosphor stripes 30 are excited to luminescense by electron beams projected by a plurality of electron guns which may comprise a triad of guns located in the neck region of the cathode ray tube envelope (not shown). The phosphors comprise red-light-emitting, green-light-emitting, and blue-light-emitting compositions, each of which is excited by an associated beam which falls upon the proper phosphor pattern in passage through the perforations 28 of shadow mask 15.
The well-known process of successive application of color phosphors and other screening fluids to the screen-bearing surface 22 of the face panel 12 requires that the shadow mask assembly 10 be removed and inserted in proper registration with the face panel 12 and associated phosphor stripes 30 several times during manufacture. Although the mask can be inserted into and removed from the face panel manually, it is far more efficient to perform the operation by an automatic apparatus. By its nature, such an apparatus is quicker, more positive in operation, and is less likely to damage the face panel and/or the mask in the mask insertion operation. Also, foreign matter such as human hair and airborne dust is less likely to fall onto critical areas of the mask or panel. The presence of such foreign matter in active areas of the face panel assembly can result in rejection during final testing of the cathode ray tube of which the assembly is a part.
As has been noted, for a successful insertion, the suspension spring apertures 20 must be brought into alignment with the studs 14 before the springs 18 can be released to make engagement with the studs. A major constraint in the design of automatic shadow mask inserters are the unpredictable deviations in the dimensions of both the suspension system of the shadow mask and the stud locations which have, precluded positive, consistent and unequivocal engagement of apertures with studs. The deviations may be as much as 0.050 inch in the suspension system and 0.075 inch in the studs for a 19-inch cathode ray tube. The dimensional deviations of the mask for example have their origin in differences of the length of springs, spring curvatures, shadow mask frame dimensions, and the relatively imprecise location of the points of attachment of the springs with respect to the shadow mask frame. As a result, there is no reliable reference location on the mask assembly from which to determine the location of the spring apertures. Due to the potential for buildup in production tolerances, it cannot be assumed that either the spring apertures or the studs are located at predetermined fixed points. A condition of mis-alignment may result wherein at least one spring aperture may entirely escape engagement with its associated stud. When this occurs, it usually becomes necessary to stop the production line; the cost of such stoppage may be as much as $100 per minute of down time. Further, if the mis-engagement is not detected at the mask-inserter station, the defective assembly may continue down the production line to some station where the mask may actually fall out of the panel and damage the mask-panel assembly and/or the production apparatus itself.
Because of the unpredictable deviations in dimensions and the potential buildup of tolerances consequent thereto, the design and fabrication of reliable mask-inserter apparatus has been fraught with problems. The mask-inserter apparatus may, for example, successfully insert the mask into the panel 999 times out of 1,000. The seemingly high reliability is totally unacceptable because it may mean that it will be necessary to stop the production line as many as forty times during a 24-hour period. Achieving a cost-effective level of reliability has hitherto been difficult to the point of insurmountability in the design of mask inserters.
U.S. Pat. No. 3,899,812, Baranski, et al, of common ownership herewith, discloses automatic apparatus for inserting a CRT mask into its mating panel. Means are included which are intended to align the shadow mask such that the mask alignment holes are positioned at the points which lie in a substantially horizontal hole reference plane with each hole positioned at a predetermined location. Means are provided for engaging the panel studs and aligning the panel by means of the studs to a position where the studs are located at points which lie in substantially horizontal stud reference plane. The studs are at a location within that plane which places each stud in vertical alignment with and at a predetermined distance of its corresponding shadow mask alignment hole. With the shadow mask and its panel in positions of alignment, the mask springs are depressed to permit insertion of the mask assembly into the panel. The mask is then raised to the predetermined distance between the hole reference plane and the stud reference plane, and the springs are released to permit engagement between each stud and its corresponding alignment hole. Stud-locating fingers, and hole-locating pins, are intended to provide for mutual positioning of the panel and the mask, respectively, in the corresponding reference planes. U.S. Pat. No. 3,838,483, also to Baranski, et al, also of common ownership herewith, describes a method for inserting a CRT mask into its mating panel by means of the apparatus set forth in the aforedescribed '812 patent.
In U.S. Pat. No. 4,188,695 to Oyama, there is disclosed mask-inserter apparatus wherein means are provided for detecting an inserted shadow mask that is incompletely fitted, due to failure of one or more of the suspension springs to engage the associated stud. The apparatus comprises panel height-variation-detection means for detecting height variations in different portions of the mask when the shadow mask is incompletely fitted to the panel. The height variation detection means consist of photo-switches, limit switches, or proximity switches.
In U.S. Pat. No. 4,130,919, Oyama discloses an apparatus for removing a shadow mask assembly from a panel, and inserting the mask into a dummy panel. The dummy panel provides for the protective storage or shipment of the mask. The apparatus includes means for mo ing the mask-panel assembly to a work station, depressing the suspension springs that detachably engage the mask to the panel, transporting the panel from the station, removing the mask from the panel, and inserting the mask into the dummy panel. The suspension springs are depressed by pawls which bend the springs for disengagement of the mask from the panel. The apparatus can be designed to process mask-panel assemblies having suspension means located on three sides, or on four sides of a mask. There is no requirement for the precision engagement of the mask with the dummy panel typical of the mask-face panel assembly means described herein.
U.S. Pat. No. 4,164,060 to Hartta discloses an apparatus for assembling a shadow mask and panel of a television receiver picture tube. The apparatus is provided with separate supports for the mask and panel, with one of the supports being made as a "floating plate" movable relative to the other fixed support parallel to its plane and also perpendicularly to the plane. In addition, the floating plate is rotatable around an axis perpendicular to a plane. It is reputed that while the mask and panel may be positioned only roughly in register on the apparatus, the mechanical moving of the floating plate brings the mask and panel in such a relative position that their fixing members automatically engage each other.